BIOLOGY 1M03 Test 2

Biological species concept

Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups (reproductive isolation)

Downsides of the biological species concept

Difficult to apply to asexually reproducing organisms, fossils, and hybrids

Prezygotic isolation factor

Barriers preventing species' from mating prior to zygote formation

Postzygotic isolation factor

Barrier preventing species' from reproducing viable and fertile offspring

Examples of prezygotic isolation factors

1. Temporal (timing)

2. Ecological (spacial)

3. Mechanical (reproductive organs are incompatible)

4. Gametic (gametes are incompatible)

5. Behavioural (mating rituals)

Examples of postzygotic isolation factors

1. Hybrid inviability (zygote does not develop)

2. Hybrid sterility (zygote is sterile)

Issues with the biological species concept: hybridization

- hybrids don't always look like the parental species, but it is not a distinct species

- sometimes able to reproduce with the parental species, however, they are normally selected against

Morphospecies concept

members of the same species usually look alike

Benefits of the morphospecies concept

1. applicable for fossils

2. applicable for asexually reproducing organisms

Downfalls of the morphospecies concept

1. 2 distinct species may look similar, and thereby falsely classified as 1 species

2. 1 species may vary, thereby falsely being classified as 2 species

3. 2 species may not have visible differences

Ecological species concept

Species are classified by how they interact with the environment

Is it possible for 2 species to coexist in the same location if they have similar niches?

NO

Downfalls of the ecological species concept

Sometimes males and females of the same species have varying niches

Niche

The range of conditions a species can tolerate and how it interacts with its environment

Phylogenetic species concept

Members of a species all share a common ancestry and a common fate

Speciation

Byproduct of genetic divergence that occurs as a result of the fixation of different mutation in 2 populations that are not regularly exchanging genes

Allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

Allopatric speciation mechansisms

Dispersal and vicariance

Dispersal

When individuals colonize a distant place, far away and isolated from the source population

Vicariance

Allopatric speciation caused by the formation of a geographic barrier, separating a population into 2

Peripatric speciation

Few individuals from a mainland population disperse to a new location remote from the original and evolve separately

Island population

Patch of habitat on the mainland that is appropriate for the species but remote from the mainland's habitat

Adaptive Radiation

Rapid evolutionary diversification in which natural selection accelerates the rates of both speciation and adaptation to fulfil ecological niches

Co-speciation

A process in which 2 groups of organisms speciate in response to each other and at the same time

Sympatric speciation

Speciation occurring in the same location

How does sympatric speciation arise?

Disruptive selection

Instantaneous speciation

Caused by the hybridization between 2 species in which the offspring are reproductively isolated from both parents

Tetraploid

When the offspring receives a full set of chromosomes from both parents, meaning they have double the diploid number of their parents

What organism is tetraploidy common in?

Plants

Allopolyploid

Multiple sets of chromosomes from DIFFERENT species

Autopolyploid

An individual that has more than two chromosome sets that are all derived from a SINGLE species

What is the phylogenetic species concept based on?

Monophyletic groups; a species is the smallest monophyletic group

Synapomorphy

Shared derived trait

How are monophyletic groups identified?

Synapomorphies

Genetic synapomorphy

Mutation shared by all members of a monophyletic group

Pros of the phylogenetic species concept

1. Can be applied to any type of population

2. Logical: different species have different synapomorphies due to a lack of gene flow and independent evolutions

Cons of the phylogenetic species concept

- Phylogenies are currently available for only a tiny subset of populations on the tree of life

- Different gene trees can be discordant; some genes in the genome may be consistent with different relationships among groups

- May lead to recognition of many more species than either of the other species concepts

Incomplete lineage sorting

gene trees do not always match species trees (gene tree discordance)

Coalescence

Common ancestor

How are species trees generated?

By evaluating entire genomes

Subspecies

Populations that are not distinct enough to be considered a separate species

Traits of a subspecies

- live in a discrete geographic areas

- have distinguishing features

- can interbreed if geographical barriers are removed

What causes allopatric speciation?

Reduced gene flow between populations, causing genetic isolation

Biogeography

The study of how species and populations are distributed geographically

What does it mean to live in sympatry?

To live close enough to possibly interbreed

2 mechanisms of sympatric speciation

External and internal events

What causes sympatric speciation?

Isolation caused by different ecological niches

Instantaneous speciation

Speciation that occurs in a single generation

What causes instantaneous speciation?

2 species hybridize and offspring is reproductively isolated by both parental species

Polyploidization

Process by which an individual is formed with extra sets of chromosomes in cells due to accidents during meiosis or mitosis (more than 2 sets of chromosomes)

What type of speciation might polyploidization cause?

Sympatric speciation

Which is more common: autopolyploid vs allopolyploid

Allopolyploid

Are allopolyploids fertile?

Yes!

Are autopolyploids reproductively isolated from parents?

Yes!

Offspring between a tetraploid and a diploid are______.

sterile

Outcome of hybridization from 2 diploid species

Tetraploid; often sterile

Who have higher levels of heterozygosity?

Polyploids (not as affected by inbreeding depression)

Phylogenetic tree

A family tree that shows the evolutionary relationships thought to exist among groups of organisms

Monophyletic group

A group that shares a common ancestor

Root of phylogenetic tree

Most ancestral branch

Outgroup (phylogenetic tree)

Sister group that shares a recent common ancestor, but is not part of the group of focus

Polytomy (phylogenetic tree)

A node that divides into 3 or more branches suggesting that not enough data were available to resolve which taxa are most closely related

Extant taxa (currently living)

Located at branch tips; none of the extant taxa are presumptive ancestors of the others

Sister groups

Closely related taxa

Trait

Genetic (typically DNA), morphological, physiological or behavioural characteristic to be studied

What is an outgroup used to determine?

Whether a trait is ancestral or derived

Ancestral trait

A trait that existed in the ancestor

Derived trait

A modified form of the ancestral trait, found in a descendant

How do derived traits arise?

Mutation, selection, genetic drift

Cladistics

First formal method to infer phylogenetic trees; based on reconstructing relationships species by identifying synapomorphies

Maximum parsimony

The principle that states the most likely explanation or pattern is the one that implies the least amount of change

Homology

Similar traits due to shared ancestry.

Homoplasy

Similar traits, not caused by common ancestry

Are water lilies and wild roses a product of convergent or divergent evolution?

Divergent

Are Streamlined Bodies in Dolphins and Ichthyosaurs Homologous or Convergent?

Convergent

Adaptive radiation

The rapid production, from a single lineage, of many descendant species

3 hallmarks of adaptive radiation

1. they are a monophyletic group

2. they speciated rapidly

3. they diversified ecologically into many niches

2 mechanisms that can trigger adaptive raditations

1. Extrinsic factors such as a favourable new condition in the environment or access to a new environment

2. Intrinsic factors such as evolution of key morphological, behavioural, physiological...

Ecological opportunity

The availability of new or novel types of resources - has driven a wide array of adaptive radiations

4 hypotheses for the start of the Cambrian explosion

1. higher oxygen levels

2. evolution of predation

3. new niches beget more new niches

4. new genes, new bodies

Hominids

Great apes

Bipedal

The ability to walk upright on two legs

How do oranguatans walk?

Fist-walk

How do gorillas, bonobos, and chimps walk?

Knuckle-walk

Bipedalism

The synapomorphy that defines the hominins

When and where did the common ancestor of chimps and humans live?

6-7 million years ago; Africa

4 hominin groups

1. Gracile australopithecines

2. Robust australopithecines

3. Early homo

4. Recent homo

Ardipithecus

Combo of tree climbing and bipedal activity; protruding mouth and nose shape

Gracile australopithecus

Small bipeds with small teeth; more ape-like appearance

Robust Australopithecus (Paranthropus)

Small bipeds with big teeth; prolly ate plants

Homo genus (early)

Larger braincase than australopithecines; reduced cheek teeth

Homo genus (recent)

Even larger braincases

H. neanderthalensis

Last hominin species to live at the same time as humans; heavy build, large brains, low foreheads, powerful jaws, large browridges, small chins

Homo sapiens

Reduced browridge, flat face, largest braincase

Pros of a large brain

Allows for more complex behaviours and language

General skull evolution trend

Flatter and larger over time

What can be deduced from the fossil record about hominins?

1. shared feature that defines hominins is bipedalism

2. the hominin family tree has many branches - there was not a linear progression from one species to another

3. species in the genus homo have extremely large brain cases in comparison to their overall body size

Hypothesis for larger braincase

Natural selection selected for larger brains because it allowed individuals to communicate and work with tools

Out-of-Africa hypothesis

The hypothesis that modern humans (Homo sapiens) evolved its distinct traits in Africa and then spread to other continents; H. sapiens evolved independently of earlier European and Asian species of Homo

What can the fossil record NOT support regarding the out-of-africa hypothesis?

Whether or not there was inbreeding with Neanderthals